X-ray Diagnostics and Their Relationship to Magnetic Fields David Cohen Swarthmore College

XMM-Newton Chandra Launched 2000: superior sensitivity, spatial resolution, and spectral resolution sub-arcsecond resolution

XMM-Newton Chandra Both have CCD detectors for imaging spectroscopy: low spectral resolution: R ~ 20 to 50 And both have grating spectrometers: R ~ few 100 to 1000

 1 Ori C Chandra ACIS Orion Nebula Cluster (COUP) Color coded according to photon energy (red: 2 keV)

Stelzer et al  1 Ori C: X-ray lightcurve

 Ori E: XMM light curve Sanz-Forcada et al. 2004

XMM EPIC spectrum of  Ori E Sanz-Forcada et al. 2004

 Pup  1 Ori C Chandra grating specra:  1 Ori C and a non-magnetic O star

Hot plasma emitting thermal x-rays 1 keV ~ 12 × 10 6 K ~ 12 Å ROSAT 150 eV to 2 keV Chandra, XMM 350 eV to 10 keV Shock heating:  v = 300 km gives T ~ 10 6 K (and T ~ v 2 )

Hot plasma emitting thermal x-rays 1 keV ~ 12 × 10 6 K ~ 12 Å ROSAT 150 eV to 2 keV Chandra, XMM 350 eV to 10 keV Shock heating:  v = 1000 km gives T ~ 10 7 K (and T ~ v 2 )

 Pup  1 Ori C Si XIII Si XIV Mg XI Mg XII H-like/He-like ratio is temperature sensitive

 Pup  1 Ori C Si XIII Si XIV Mg XI Mg XII The magnetic O star –  1 Ori C – is hotter

Differential Emission Measure (temperature distribution) Wojdowski & Schulz (2005)  1 Ori C is much hotter

1000 km s -1 Emission lines are significantly narrower, too  1 Ori C (O7 V)  Pup (O4 If)

Wade et al Dipole magnetic field

Shore & Brown, 1990

Rotating tilted dipole Simulation/visualization courtesy R. Townsend

temperature emission measure MHD simulations of magnetically channeled wind Channeled collision is close to head-on:  v > 1000 km s -1 : T > 10 7 K simulations by A. ud-Doula; Gagné et al. (2005)

Differential emission measure (temperature distribution) MHD simulation of  1 Ori C reproduces the observed differential emission measure Wojdowski & Schulz (2005)

Simulation EM (10 56 cm -3 ) θ 1 Ori C ACIS-I count rate (s -1 ) Rotational phase (P= days) Chandra broadband count rate vs. rotational phase Model from MHD simulation

Simulation EM (10 56 cm -3 ) θ 1 Ori C ACIS-I count rate (s -1 ) Rotational phase (P= days) The star itself occults the hot plasma torus The closer the hot plasma is to the star, the deeper the dip in the x-ray light curve

Emission measure contour encloses T > 10 6 K

Helium-like species’ forbidden-to-intercombination line ratios – f/i or z/(x+y) – provide information about the location of the hot plasma …not the density, as is usually the case.

g.s. 1s 2 1 S 1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) eV 1-2 keV Helium-like ions (e.g. O +6, Ne +8, Mg +10, Si +12, S +14 ) – schematic energy level diagram

1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) g.s. 1s 2 1 S Ultraviolet light from the star’s photosphere drives photoexcitation out of the 3 S level UV

1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) g.s. 1s 2 1 S The f/i ratio is thus a diagnostic of the local UV mean intensity… UV

1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) g.s. 1s 2 1 S …and thus the distance of the x-ray emitting plasma from the photosphere UV

R fir =1.2 R * R fir =4.0 R * R fir =2.1 R *

He-like f/i ratios and the x-ray light curve both indicate that the hot plasma is somewhat closer to the photosphere of  1 Ori C than the MHD models predict.

Some slides showing f/i ratios in zeta Ori, tau Sco… main point: there is NO evidence for a “near star high ion problem”

 Pup S XV Chandra MEG

More possible topics: Zeta Ori, HD – magnetic but X-rays look “normal” Tau Sco – narrow lines but f/i ratios imply plasma far from the photosphere Sigma Ori E – X-ray DEM well reproduced by Rich’s RFHD modeling; flaring too (centrifugal breakout) Early B stars are mysterious – large x-ray luminosities, soft spectra, narrow lines but no evidence for magnetic fields (theta Car, beta Cru)

Conclusions Some conclusions…